I do understand. The sad truth is that there *are* kittens who need re-homing, too. I think the thing that many of us, including you, no doubt, struggle with is rationalising taking on a kitten when there are so many adult cats needing a home. The only solution is to continue to support and encourage people to be responsible and neuter their cats.
We have, in the past, adopted 4 adult cats from rescue centres. They have all been pure-bred persian and we can not believe that they have ever got to the stage of being unwanted. After our first persian, about 15 years ago, we did think fleetingly about getting a persian kitten as we thought that we could imprint it with US, if you know what I mean. However, we soon had a rethink when we realised a) how expensive they are and b) how many persian rescue centres there are, as well as how many persian cats arrive at other rescue centres. It still amazes me that people will pay between £400 and £600 for a kitten from a breeder and then pay for vaccinations, neutering (sometimes) etc etc and STILL get bored of them when they are no longer so cute and floofy.
(we are, actually, picking up two gorgeous red persian adults from a rescue centre next week!)
All of our adult cats have come to us at around the age of 5. To be totally honest, we have never had any problem whatsoever at settling them in and getting to know their amazing individual characters. And we haven't had to go through all of the jumping on to worktops, scratching the sofas stage as they've grown out of it!
But, you have to respect your partner. Just make sure that he is aware of the cost of vaccinating, neutering, deworming, etc, a kitten, as well as socialising it! It's not only money but time - he has to be really dedicated . . . . . not that I am suggesting he is not, of course! Remind him that adult cats come with all of the above - and are often more grateful that you are providing them with a lucky break in life, too!
But yes, as I said above, kittens DO need homes as well so I would suggest that you put yourself on to the kitten waiting list at your local shelter/s and prepare to be patient! I am sure that you won't have to wait too long - you can get your homecheck done whilst you are waiting!
Best of luck!